This invention relates to flexible, expandable, helical, i.e., spiral, duct for use on household appliances such as clothes dryers, etc.
Flexible helical duct, as of metal, is presently marketed for use on household appliances such as clothes dryers. Installation of the duct can be a considerable chore, however. The duct should be attached to the dryer and to the wall exhaust pipe after the dryer is in its final location. If the duct is installed when the dryer is a distance from the final location, e.g., away from the wall or along the wall, subsequent movement of the dryer often results in kinking and/or twisting and buckling of the duct. However, installation of the duct after the dryer is fully located can be extremely difficult, or even impossible, due to the lack of working space. Once helical duct is installed with the duct secured in place on both ends, subsequent movement of the dryer which causes extension or contraction or lateral movement of the flexible duct will cause twisting of the duct likely to result in buckling of the duct. This is a characteristic of helical duct. When helical duct is axially expanded, portions of the helical ridges and the helical valleys advance helically in a twisting motion. When the duct is contracted, the helical ridges and valleys twist in the opposite direction. While the duct could conceivably be made of annular segments rather than of helical character, and thereby not have the twisting tendency, such a duct would be much more expensive to fabricate and really is considered impractical for use as dryer duct or the like.
Use of the particular duct and elbow arrangements in pending applications Ser. No. 621,757, filed Dec. 4, 1990, and entitled DRYER DUCT AND VENT ASSEMBLY; Ser. No. 621,774, filed Dec. 4, 1990, and entitled UNIVERSAL DRYER DUCT AND VENT; Ser. No. 621,756, filed Dec. 4, 1990, and entitled UNIVERSAL DUCT ELBOW AND CONNECTOR PLATE; and Ser. No. 621,775, filed Dec. 4, 1990, and entitled SOFT CUFF CORRUGATED DUCT has been found to enable attachment of the duct to the wall and dryer before placement of the dryer in its ultimate location, and to enable movement of the dryer after placement, if necessary, without twisting and buckling of the duct. Indeed, these arrangements have been found to enable the helical duct to be axially expandable and contractible, and laterally shiftable without buckling. The arrangements disclosed in the above applications enable rotation between portions of the duct, which alleviates the torque that would otherwise occur to cause buckling of the fixed end ducts. This present development is an extension of the developments disclosed in these earlier applications.